Compositions which contain polybutylene terephthalate and barium sulfate have been described in U.S. Pat. No. 4,043,971. These compositions were characterized as having improved tracking resistance as compared to polybutylene terephthalate that did not contain any filler when measured in a standard test. The amounts of filler which are taught in U.S. Pat. No. 4,043,971 are from 5-60% by total weight of composition. This patent also notes additives and stabilizers may be present in the improved tracking resistant compositions but no embodiments of these components are exemplified. Compositions of polybutylene terephthalate and polyethylene terephthalate with fillers are disclosed in U.S. Pat. No. 3,953,394.
The surface of a composition which consists of polybutylene terephthalate and 60%, by total weight of composition, of barium sulfate is not particularly glossy due to the high level of filler and is undesirable for use in preparing molded articles such as tableware which require a smooth surface. The applicants have discovered that if polyethylene terephthalate is added to the composition of polybutylene terephthalate and barium sulfate, the tracking resistance degrades but the surface properties improve. In addition to having a smooth and glossy surface, objects molded from these compositions which contain high levels of barium sulfate have a ceramic-like feel and appearance because of the smooth, glossy surface and the density of the composition which is greater than 2.0. This composition has special utility for the injection molding of articles such as tableware including dishes, bowls or mugs; billiard balls, poker chips, paper weights, wall or floor tiles and the like. These articles have superior stain resistance and are opaque to x-rays.
Compositions within the scope of the invention will pass an FDA extractables test when prepared with a suitable grade of barium sulfate such as barium sulfate, U.S.P.
The compositions of the invention may be used to mold circuit boards or panels. The molded articles are essentially warp free, have excellent creep resistance, a low coefficient of thermal expansion and a high heat distortion temperature.
Barium sulfate is non-toxic and insoluble in dilute acids which make it uniquely suitable for containers which will come in contact with acid foods. Other inorganic fillers such as zinc oxide, titanium dioxide, calcium carbonate are either soluble in dilute acid or will react with dilute acid which makes these materials unsuitable for direct contact with certain food stuffs. For those applications, a resin rich surface is required. Barium sulfate is readily available in highly pure form and is unaffected by conventional microwave cooking.
Accordingly, it is an object of this invention to provide a molding composition which contains high levels of barium sulfate which when molded will have a smooth and glossy surface.
It is also an object of this invention to provide novel molding compositions which have a ceramic-like feel and density.
It is also an object of this invention to provide novel molding compositions which have a special utility for molded articles such as tableware.
It is also an object of this invention to provide a novel molding composition which can be fabricated into objects that are not affected by microwaves and are thus suitable for use during microwave cooking. These and other objects will become apparent from the present specification.